Embodiments of the present invention relate to systems and methods for modulation of an optical signal. More specifically, embodiments of the present invention relate to the design and methods of operation of a laser source and laser projection system to reduce the presence of speckle that may be visible in a laser projection image. Speckle may result whenever a coherent light source is used to illuminate a rough surface, for example, a screen, or any other object that produces a diffused reflection or transmission.
Particularly, a multitude of small areas of the screen or other reflecting object scatter light into a multitude of reflected beams with different points of origination and different propagation directions. At an observation point, for example in the observer's eye or at the sensor of a camera, these beams interfere constructively to form a bright spot, or destructively to form a dark spot, producing a random granular intensity pattern known as speckle. Speckle may be characterized by the grain size and contrast, usually defined as a ratio of standard deviation to mean light intensity in the observation plane. For a large enough illuminated area and a small enough individual scattering point size, the speckle will be “fully developed,” with a brightness standard deviation of 100%. If an image is formed on the screen using laser beams, such granular structure will represent noise, or a serious degradation of the image quality.